1. Field of the Invention
The present invention relates to a color cathode-ray tube, and more particularly, to an electron gun having an improved shield cup to improve the deflection (defocusing or aberration) or coma, and a color cathode-ray tube using the same.
2. Description of the Related Art
FIG. 1 shows a cathode-ray tube employing a deflection yoke of self-convergence, the cathode-ray tube used for televisions and monitors. As shown in FIG. 1, a color cathode-ray tube 10 includes a panel 12 having a phosphor screen 11, on which red, green and blue phosphor materials are provided in a dotted or striped pattern, in the inside; a funnel 13 which includes a neck portion 13a and a cone portion 13b and is fastened to the panel 12; an electron gun 20 housed in the neck portion 13a of the funnel 13; and a deflection yoke 15 provided throughout the cone portion 13b of the funnel 13 to deflect electron beams emitted from the electron gun 20.
As shown in FIG. 2, the electron gun 20 includes three cathodes 21 arranged in line, a plurality of electrodes 22 which are spaced apart from the cathodes 21 by a predetermined distance and having three electron beam passages arranged in line, a final accelerating electrode 23, and a shield cup 24 provided on the final accelerating electrode 23.
In the color cathode-ray tube 10 having such a configuration, three electron beams emitted from the electron gun 20 are selectively deflected by the deflection yoke 15 and land on the phosphor screen 11, exciting phosphor materials, so that an image is displayed.
During this procedure, a deflection magnetic field deflecting electron beams emitted from the electron gun 20 is composed of a pincushion-shaped horizontal deflection magnetic field HB and a barrel-shaped vertical deflection magnetic field VB, as shown in FIG. 3, so that it can converge the three beams arranged in line to the phosphor screen 11 without additional dynamic convergence. However, as shown in FIG. 4, the flux density of a magnetic field formed by a deflection yoke increases from the center toward the periphery in a horizontal direction, so the cross-sections of the red (R) and blue (B) electron beams, among the three electron beams (R, G and B electron beams) arranged in line, are distorted. In other words, as shown in FIG. 5, the R and B electron beams are subjected to forces in arrow headed directions by the pincushion magnetic field HB of a deflection yoke, so that halos are formed around the R and B electron beams. A halo phenomenon appearing in the R and B electron beams becomes worse toward the periphery of a phosphor screen, as shown in FIG. 6. Accordingly, the magnitude of an electron beam landing on the periphery of the phosphor screen changes. The halo phenomenon of an electron beam and the non-uniformity of the cross-section of the electron beam degrade the resolution of an image formed by exciting the phosphor screen.
Examples of an electron gun for reducing the problem of a coma are disclosed in Japanese Patent Publication No. Hei 4-52586, Japanese Patent Laid-open No. Sho 51-61766, Japanese Patent Laid-open No. Sho 51-64368 and Japanese Patent Publication No. Hei 10-116569.
According to the disclosed technical configurations, upper and lower flat electrodes narrowing the paths of three electron beams are disposed on the bottom face of a shield cup of an in-line type electron gun, parallel to the in-line direction of the electron beams and extending toward a main lens or a phosphor screen. Alternatively, an electron gun is designed such that an electrostatic quadrupole lens is formed between some electrodes, and the strength of the electrostatic quadrupole lens varies with a deflection signal corresponding to the deflection of an electron beam, thereby achieving uniformity of an image over the entire screen. In another example, an astigmatic lens is provided in a region between electrodes forming a prefocus lens to achieve the uniformity of the cross-section of an electron beam over the entire phosphor screen. In still another example, the electron beam passages of first and second electrodes of an electron gun have different aspect ratios, thereby preventing the distortion of electron beams landing on the center and periphery of a phosphor screen.
Japanese Patent Publication No. Hei 10-116570 discloses a configuration for correcting the deflection of electron beams, in which magnetic pieces are partially disposed in electrodes forming an electron gun installed in the neck portion of a cathode-ray tube, and a magnetic field generating device is disposed on the outer surface of the neck portion, thereby generating a magnetic field synchronized with a deflection signal and exciting the magnetic pieces.
U.S. Pat. No. 5,912,530 discloses a configuration for correcting deflection using a deflection magnetic field, in which left and right magnetic pieces are disposed in one of the electrodes of an electron gun emitting three electron beams in line, and magnetic pieces are disposed between a center electron beam and peripheral electron beams.
U.S. Pat. No. 5,818,156 discloses a configuration for correcting deflection, in which magnetic materials are attached to the upper and lower portions of each of the side electron beam passages in a shield electrode within a deflection magnetic field.
As described above, when the shape of an electron beam passage is transformed or the magnifying power of an electron lens is varied in synchronization with a signal applied to a deflection yoke, to correct the deflection of an electron beam using a deflection magnetic field, it is difficult to manufacture an electron gun and control electron beams. In addition, when magnetic pieces are attached to both sides of each of the electron beam passages arranged on the bottom face of a shield cup in line and attached between the electron beam passages, the complexity of the shape of the magnetic pieces causes excessive dissemination depending on the shape of parts and result in difficult assembly, thereby disturbing the improvement of productivity.
To solve the above problems, it is an object of the present invention to provide an in-line type electron gun for reducing deflection (defocusing or aberration) or coma due to the non-uniform magnetic field of a deflection yoke and reducing a voltage difference due to the deflection of side electron beams arranged in line, thereby improving the resolution of an image throughout a phosphor screen, and a color cathode-ray tube using the electron gun.
Accordingly, to achieve the above object of the invention, in first aspect, there is provided an electron gun for a color cathode-ray tube. The electron gun includes cathodes arranged in line, a plurality of electrodes sequentially disposed from the cathodes and having electron beam passages for passing three electron beams, a shield cup coupled to a last electrode among the plurality of electrodes and provided with three electron beam passages in line, and at least one coma correction portion disposed on the shield cup or one or more electrodes among the plurality of electrodes in such a manner of positioning the coma correction portion above and below the spaces between the center of a central electron beam passage and the centers of side electron beam passages.
In second aspect, there is provided an electron gun for a color cathode-ray is tube. The electron gun includes three cathodes arranged in line, a control electrode, a screen electrode, a plurality of focus electrodes sequentially disposed from the screen electrode and forming an auxiliary lens and a main lens, a final accelerating electrode, a shield cup coupled to the final accelerating electrode and provided with three electron beam passages arranged in line, and at least a pair of coma correction portions which are disposed on the shield cup or one among the plurality of focus electrodes in such a manner of positioning the centers of magnetic pieces above and below the spaces between the center of a central electron beam passage and the centers of side electron beam passages among the three electron beam passages formed on the control electrode and the screen electrode.
In third aspect, there is provided an electron gun for a color cathode-ray tube, including three cathodes arranged in line; a control electrode and a screen electrode which are sequentially disposed from the cathodes; a plurality of focus electrodes sequentially disposed from the screen electrode and to which a dynamic focus voltage synchronized with a deflection signal is applied, thus forming a quadrupole lens; a final accelerating electrode disposed to be adjacent to the focus electrodes and forming a main lens; a shield cup coupled to the final accelerating electrode and provided with three electron beam passages arranged in line; and at least a pair of magnetic pieces which are disposed on the shield cup or one among the plurality of focus electrodes in such a manner of positioning the magnetic pieces above and below the spaces between the center of a central electron beam passage and the centers of side electron beam passages among the three electron beam passages formed on the control electrode, the screen electrode and a shield cup.
To achieve the above object of the invention, there is also provided a color cathode-ray tube including a housing including a panel having a phosphor screen on its inside and a funnel fastened to the panel, the funnel including a neck portion; an electron gun housed in the neck portion and emitting electron beams for exciting the phosphor screen and forming an image, the electron gun including cathodes arranged in line, a plurality of electrodes sequentially disposed from the cathodes and having electron beam passages for passing three electron beams, a shield cup coupled to a last electrode among the plurality of electrodes and provided with three electron beam passages in line, and magnetic pieces disposed on the shield cup or one or more electrodes among the plurality of electrodes in such a manner of positioning the magnetic pieces above and below the spaces between the center of a central electron beam passage and the centers of side electron beam passages; and a deflection yoke disposed throughout the neck and cone portions of the funnel, the deflection yoke deflecting electron beams emitted from the electron gun to phosphor positions on the phosphor screen.
Preferably, the magnetic pieces constructing the comma correction portion have a circular plate shape or a polygonal shape, the diameter of the magnetic pieces is 1 mm or more and 4 mm or less, and the thickness of the magnetic pieces is 0.1 mm or more and 2.0 mm or less. Preferably, a magnetic field distribution formed by the pair of coma correction portions is symmetric with respect to a direction in which the electron beam passages arranged in line on the shield cup or the electrodes.